Abstract
The role of human UDP glucuronosyltransferase (UGT) 2B10 in the N-glucuronidation of a number of tricyclic antidepressants was investigated and compared with that of UGT1A4 in both the Sf9 expressed system and human liver microsomes. The apparent Km (S50) values for the formation of quaternary N-glucuronides of amitriptyline, imipramine, clomipramine, and trimipramine were 2.60, 16.8, 14.4, and 11.2 μM in UGT2B10 and 448, 262, 112, and 258 μM in UGT1A4, respectively. The kinetics of amitriptyline and imipramine glucuronidation in human liver microsomes exhibited a biphasic character, where the high- and low-affinity components were in good agreement with our results in expressed UGT2B10 and UGT1A4, respectively. The kinetics of clomipramine and trimipramine glucuronidation in human liver microsomes were sigmoidal in nature, and the S50 values were similar to those found for expressed UGT1A4. The in vitro clearances (CLint or CLmax) were comparable between UGT2B10 and UGT1A4 for glucuronidation of imipramine, clomipramine, and trimipramine, whereas CLint of amitriptyline glucuronidation by UGT2B10 was more than 10-fold higher than that by UGT1A4. Nicotine was found to selectively inhibit UGT2B10 but not UGT1A4 activity. At a low tricyclic antidepressant concentration, nicotine inhibited their glucuronidation by 33 to 50% in human liver microsomes. Our results suggest that human UGT2B10 is a high-affinity enzyme for tricyclic antidepressant glucuronidation and is likely to be a major UGT isoform responsible for the glucuronidation of these drugs at therapeutic concentrations in vivo.
Footnotes
Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
doi:10.1124/dmd.109.030981.
-
- UGT
- uridine diphosphate glucuronosyltransferase
- UDPGA
- uridine 5′-diphosphoglucuronic acid
- TCA
- tricyclic antidepressants
- HLM
- human liver microsome(s)
- PCR
- polymerase chain reaction
- bis-Tris
- 2-[bis(2-hydroxyethyl)amino]-2-(hydroxymethyl)propane-1,3-diol
- MOPS
- 4-morpholinepropanesulfonic acid.
- Received October 30, 2009.
- Accepted February 4, 2010.
- Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics
DMD articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|